In recent years, in electronic or electrical equipment (hereinafter, which may be simply referred to as electronic/electrical equipment), various performances, for example, heat resistance, mechanical properties, chemical properties, and electrical properties are become to be further highly enhanced more than ever before in those equipment, thus reliability has become required to be enhanced more than ever before in those equipment.
On the other hand, the electronic/electrical equipment represented by motors or transformers, has been progressed resulting in size reduction and improved performance in recent years. Thus, it becomes usual in many cases that insulated wires are used in such a way that the insulated wires are processed by winding (coil processing) to be winding wires and they are pushed into a quite small space to pack. Specifically, in order to enhance the performances of the rotating electrical machine, such as a motor, it is requested that how many winding wires produced above can be stored into a stator slot. That is, enhancement of the ratio of the sectional area of conductors to the sectional area of the stator slot (i.e. the space factor) has been required to be highly increased.
As a means for increasing the space factor, it has been lately attempted to use a rectangular wire in which the conductor has a cross-sectional shape similar to a quadrilateral (square or rectangle).
However, the use of the rectangular wire achieves a drastic effect on improvement of the space factor, while the corner having a rectangular cross-sectional shape is extremely vulnerable to bending, such as coil processing. Thus, there is a problem that a coating break occurs when processed under a strong pressure. In particular, it is known that with decrease in the curvature radius of the corner, breakage of the coating due to the bending becomes easy to occur.
Further, if enough distance between conductors cannot be secured by, for example, thinning the covering layer of the winding wire, insulating performances cannot be secured and also when the covering layer of the winding wire was damaged, this results in discharge from the exposed conductor of the winding wire.
In order to solve the forgoing problem, it is proposed to change the thickness of the covering layer on the conductor having a quadrilateral cross-sectional shape in a manner such that a protruding streak protruded on one side of the surface is formed and a concave groove to which the protruding streak can be inserted is formed on a backing surface side to said one side of the surface (see Patent Literature 1).